A colony of dogs heterozygous with respect to the gene responsible for cyclic neutropenia, anemia and thrombocytopenia will be expanded. Homozygote offspring will be used to study, via bone marrow transplanatation between normal and affected dogs, the exact nature of the hematopoietic defect. Erythropoietin , thrombopoietin, and leukopoietic factors will be assayed at all stages of the neutropenic cycles of cyclically neutropenic dogs and in dogs bearing bone marrow transplants from cyclically neutropenic dogs. The interrelationships of hematopoietic factors (erythropoietic, thrombopoietic, and leukopoietic) will be studied throughout the neutropenic cycles.